Grade 7 Mathematics
PERCENT means "per hundred." To find a percent of a number, convert the percent to a decimal (divide by 100), then MULTIPLY.
Example: 25% of 80 = 0.25 x 80 = 20
Tax/Tip/Markup: Amount = Original x Rate (as decimal)
Discount: Sale Price = Original - (Original x Rate)
Percent Change: (New - Original) / Original x 100
Simple Interest: I = P x r x t
Restaurant Problem: Your meal costs $35. Calculate 7% tax and 20% tip.
Convert percent to decimal: 7% = 0.07 and 20% = 0.20
Calculate tax: Tax = 0.07 x $35 = $2.45
Calculate tip: Tip = 0.20 x $35 = $7.00
Find total: $35 + $2.45 + $7.00 = $44.45
A jacket costs $80 and is 25% off. What's the sale price?
Method 1: Find discount, then subtract
Discount = 0.25 x $80 = $20
Sale price = $80 - $20 = $60
Method 2: Shortcut - Find what percent you PAY
If 25% off, you pay 100% - 25% = 75%
Sale price = 0.75 x $80 = $60
WRONG: A price went from $50 to $60. The increase is $10, so the percent increase is 10/60 = 16.7%.
RIGHT: Percent change = (New - Original) / ORIGINAL x 100 = (60-50)/50 x 100 = 10/50 x 100 = 20%. Always divide by the ORIGINAL amount!
Formula: Percent Change = (New - Original) / Original x 100
Percent Increase Example: Population grew from 800 to 1,000
Change = 1,000 - 800 = 200 (increase)
Percent increase = 200/800 x 100 = 25%
Percent Decrease Example: Price dropped from $120 to $90
Change = 120 - 90 = 30 (decrease)
Percent decrease = 30/120 x 100 = 25%
I = Interest | P = Principal (starting $) | r = Rate (decimal) | t = Time (years)
You deposit $600 at 5% annual interest for 4 years. How much interest do you earn?
Identify: P = $600, r = 5% = 0.05, t = 4 years
Calculate: I = 600 x 0.05 x 4 = $120
Total in account: $600 + $120 = $720
1. A video game costs $50. If the sales tax is 6%, what is the total cost?
Tax amount: $ Total: $
2. A bike is on sale for 30% off. The original price is $150. What is the sale price?
Discount: $ Sale Price: $
3. A town's population increased from 5,000 to 6,500. What is the percent increase?
Change: Percent increase: %
4. Calculate the simple interest on $800 at 3% for 5 years.
I = P x r x t = x x = $